Secrets behind the Dewey Decimal Number revealed


By Jimmie Epling
Darlington County Library System

Do you remember those trips to your school’s library or the Darlington County Library System in younger days? When you asked the librarian to help you find a book, did the librarian escort you to the library’s catalog? Depending on your age, you went to a beautifully crafted oak cabinet with lots of drawers filled with thousands of cards (do you remember the subjects of the cards that looked the most grungy and frayed) or to a computer terminal, known in library talk, as a Public Access Catalog (PAC). Regardless of the catalog, when you found the book you needed for your research paper, theme, or essay, it came with a seemingly mysterious combination of numbers and letters you were told would help you find it. So with your number in hand, the librarian guided you into (or at least pointed to) “the stacks” (library jargon for shelves) in search of that special book. Likely you were so elated when you spotted that book on the shelf, you checked it out and went on your way, believing there were some arcane and mysterious secrets behind how the book got that “Dewey Decimal number” on its spine. There isn’t.

When you visit a public or school library today you will discover the non-fiction section (library jargon) is arranged by Dewey numbers. The Dewey Decimal System (DDS) can initially be a bit mysterious and perplexing to those not familiar with the library world. But don’t worry, it will all be clear to you shortly! First, there are no deep, dark secrets you must master to understand the Dewey number system. You don’t need to know how and why a seemingly random combination of numbers and letters is assigned to an item to successfully use it. Trust us, there is a kind of order and logic behind classifying items according to Dewey at the Library.

It all started with Melvil (no typo, actual spelling) Dewey in 1876 when he published “A Classification and Subject Index for Cataloguing and Arranging the Books and Pamphlets of a Library.” His goal was to create a system for classifying all knowledge using numbers and a single decimal point thrown into the mix. The system, which was later named for him, was intended to group similar books together. To do this, he decided all knowledge could be divided into 10 broad categories, 100 divisions, and 1,000 sections. What started as a system of only three numbers for each book expanded to one that can include a near endless string of numbers after the decimal point and a second line of letters and numbers below it. If you wanted, you could create a catalog number so hideously long it would wrap around the book! At the Library we use a “lite” version of Dewey to classify our items. That said, let’s start your dollar tour of today’s version of the Dewey Decimal system.

Oddly, Dewey decided those things that couldn’t easily be assigned elsewhere needed to be put at the very beginning of his classification system in a miscellaneous category called Generalities. It is a catch all for books about books, newspapers, magazines, and things you can’t quite figure where they should go (UFOs and the Abominable Snowman). All these numbers start with a “0”.

In Dewey’s world view, the next four categories deal with some aspect of mankind. First comes the 100s, which focus on the individual person with books on philosophy, psychology, metaphysics, ethics, parapsychology, occult (witchcraft, go figure), logic, and the latest Dr. Phil self-help guide. Next comes the 200s section, which revolves around our relationship with a deity or deities. Reflecting the time of its creation and likely the depth and breadth of Dewey’s personal knowledge, eight tenths of the subject headings concern Christianity. The third area of knowledge for Dewey was our relationship with one another. The 300s, Social Science, cover subjects like sociology, anthropology, government, law, true crime, education, economics, customs, etiquette, and folklore. Lastly, how we communicate with each other, the languages, received a separate classification. Once again, this section reflects Dewey in that three quarters of the subjects in the 400s concern European and Classical languages, with the balance being reserved for all other languages.
After focusing on people, Dewey’s quest to classify all knowledge turned to the world around him, the sciences and how we apply them. These two sections are the focus of the currently popular S(cience), T(echnology), E(ngineering), and M(ath) curriculum in our schools. The 500s section includes math, astronomy (a favorite subject of mine), physics, chemistry, geology, fossils (another favorite), genetics, evolution, ecology, botany, and zoology. How we apply the sciences makes up the 600s. Human endeavors related to technology, medicine, engineering, agriculture, animal husbandry, food, child care, business management, accounting, explosives, fuels, metals, furniture, textiles, and building are the subjects to be found in this section.

Once the necessities of life were classified, Dewey turned to classifying leisurely pursuits and expressions of creativity. This is why the arts make up the 700s, which includes landscaping, architecture, sculpture, coins, drawing, painting, engraving, photography, movies, music, theater, and sports. All mankind’s fiction (library speak for prose and poetry that describes imaginary events, things, and people) and that which is written about it will be found with an 800 number. Here too, pretty much eight tenths of the classifications are related to European and Classical literature and everything else is in the rest.

The last body of knowledge Dewey saw that needed classifying was geography and the recorded acts of mankind, its history. The 900s, Geography and History, are where you will find books on ancient civilizations (another favorite of mine), the Middle Ages, the history and travel guides to every country, biographies of the famous and infamous, and, in 999 (just in case we find ET or ET finds us), the geography and history of extraterrestrial worlds. In all my time in libraries, I’ve only seen one book in the 999 section and it was about our moon.

Now that the secrets of the Dewey Decimal number system have been revealed to you, the next time you delve into the Darlington County Library System’s catalog at home (online at for a specific item or visit one of our four locations to browse the shelves it will no longer appear so arcane or mysterious to you!

Author: Jana Pye

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